Proximity detection matrix display device

ABSTRACT

The invention concerns an electronic display device comprising means of detection of proximity of a conducting element situated in proximity to a display zone of the device, a set of row electrodes ( 4 ) and of column electrodes scanning the display zone, means for generating an excitation of the row electrodes and of the column electrodes as a function of an image to be displayed on the display zone. The proximity detection means comprise:
         means ( 7 ) for applying a specific electrical signal distinct from the excitation to said set,   means ( 8 ) for detecting modifications of the specific electrical signal which are induced by the presence of a conducting element in proximity to a region of the display zone,   and means ( 15 ) for determining the position of said region as a function of said detected modifications.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on International Application No.PCT/FR02/00439 filed on Feb. 5, 2002, which in turn corresponds to FR01/01941 filed on Feb. 13, 2001, and priority is hereby claimed under 35USC § 119 based on these applications. Each of these applications ishereby incorporated by reference in their entirety into thisapplication.

BACKGROUND OF THE INVENTION

The invention concerns a matrix display device comprising proximitydetection means. Such devices are used in particular for theconstruction of communication terminals of the type allowing an operatorto transmit and to receive information within the framework of afriendly exchange with a processor. The invention finds a particularapplication in respect of the screens of interactive terminalscomprising screens based on liquid crystals, on plasma, onlight-emitting diodes or on field-effect emission.

DESCRIPTION OF RELATED ART

It is known to construct such terminals by arranging one or moretransparent touch areas on the device, these being based on contact oron capacitive or inductive effect or the like. The device can then serveto delimit pressing zones of this area according to a desiredcomposition. The pressing of the area is usually done by a finger of anoperator. The visual information provided by the device is inevitablyattenuated by the add-on touch areas.

To remedy this problem, European patent EP 0 340 096 proposes that thesurface of the counter-electrode of a liquid crystal screen be used asreplacement for add-on touch areas. The surface of thiscounter-electrode is large in relation to the surface of the finger ofthe operator, this being well suited to the detection of a finger bycapacitive effect. Such an embodiment is well suited to a liquid crystalscreen comprising icons or characters which are predefined during thebuilding of the screen. By way of example, such a screen allows thedisplaying of numerical characters each composed of seven segments whichmay either be lit or unlit. A counter-electrode of this type of screengenerally covers one or more predefined locations of characters.

An embodiment in accordance with patent EP 0 340 096 cannot be used toembody a touch surface from a matrix screen comprising two arrays ofelectrodes defining, on the one hand, the rows and, on the other hand,the columns of the matrix of the screen. Specifically, such a screencomprises no counter-electrode of surface in relation to the surface ofa conducting element to be detected, as for example the finger of anoperator.

SUMMARY OF THE INVENTION

The aim of the invention is to embody in a simple manner a matrixdisplay device comprising proximity detection means. Accordingly, thesubject of the invention is an electronic display device comprisingmeans of detection of proximity of a conducting element in a displayzone of the device. Stated otherwise, the electronic display devicecomprises means of detection of proximity of a conducting elementsituated in proximity to a display zone of the device. The electronicdisplay device furthermore comprises a set of row electrodes and ofcolumn electrodes scanning the display zone, means for generating anexcitation of the row electrodes and of the column electrodes as afunction of an image to be displayed on the display zone. The displaydevice is characterized in that the proximity detection means comprise:

-   -   means for applying a specific electrical signal distinct from        the excitation to said set,    -   means for detecting modifications of the specific electrical        signal which are induced by the presence of a conducting element        in proximity to a region of the display zone,    -   and means for determining the position of said region as a        function of said detected modifications.

The devices in accordance with the invention make it possible not to fixthe pressing zones during the building of the matrix screen.Specifically, the means for detecting the position of said region candetect the presence and the position of a conducting element situated inthe immediate vicinity of the display zone. The pressing zones are nolonger limited in terms of number, dimension and position and can bepositioned and moved over the entire display zone during the usethereof. It is always of course possible to delimit the pressing zonesby a suitable display.

Furthermore, the devices in accordance with the invention make itpossible to avoid any attenuation of the visual information displayed bythe device.

DETAILED DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other advantages will becomeapparent on reading the detailed description of several embodimentsgiven by way of example. The description is illustrated by the appendeddrawing in which:

FIG. 1 a represents a front view of the structure of a matrix displaydevice;

FIG. 1 b represents this same device in profile;

FIG. 2 represents the means of the invention which are associated withone of the electrode arrays;

FIG. 3 represents an embodiment of the invention using row electrodesand also column electrodes;

FIG. 4 represents an exemplary embodiment of means for driving thedisplay, which embodiment is adapted to the invention;

FIG. 5 represents another exemplary embodiment of means for driving thedisplay, which embodiment is also adapted to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The matrix display device represented in FIGS. 1 a and 1 b comprises twoinsulating plates 1 and 2 arranged one above the other. At least one ofthe two plates 1 or 2 is transparent. The device also comprises a layer3 made from a material exhibiting electro-optical properties able totransmit or otherwise a luminous radiation under the effect of anelectrical excitation. This material comprises for example liquidcrystal. The device furthermore comprises two arrays 4 and 5 ofelectrodes. The first array 4 defines the rows of the matrix of thedevice and the second array 5 defines the columns of the matrix of thedevice. In FIG. 1 a, only a few electrodes of each array 4 and 5 havebeen represented by way of example. It is of course understood that theinvention may be implemented regardless of the number of electrodes ofeach array. By way of information, the displays commonly employed inportable screens generally comprise more than 100 electrodes per array.Advantageously, the electrodes 4 and 5 are made of a material comprisingindium-tin oxide. This material has the advantage of being transparentto luminous radiation.

The first electrode array 4 is situated between the plate 2 and thelayer 3. The second electrode array 5 is situated between the plate 1and the layer 3. The electrical excitation of the layer 3 is achieved byapplying a potential difference between an electrode of each array. Thepotential difference is, for example, due to a low-frequency AC voltageof the order of 50 to 1 000 Hertz.

Advantageously, the electrodes 4 and 5 of the two arrays areinterdigitated. More precisely, for each array, one electrode out of twois furnished with a point of electrical connection situated in thevicinity of an edge of the corresponding plate. The points of connectionof the other electrodes of the same array are situated on the oppositeedge of the same plate. This makes it possible in respect of the deviceto space out the connection points and, consequently, to increase theinsulation between two neighboring connections. The advantage affordedby the interdigitated structure for improving the detection of theposition of a conducting element will be seen later in the description.

In a first variant, described with the aid of FIG. 2, the row electrodesand the column electrodes respectively form two distinct arrays. Atleast one array is chosen for the proximity detection. The means fordetermining the position of said region define this position as afunction of the level of said modifications intervening on the chosenarray.

More precisely, the electrode array 4 is, for example, used as sensitiveelement. The display zone forms the touch surface 6. The devicecomprises electronic means 7 for generating a specific electrical signalapplied to the electrode array 4. The specific electrical signal isdistinct from the electrical excitation applied between the electrodes 4and 5 of the two arrays to modify the state of the liquid crystal.Advantageously, the specific electrical signal is a high-frequencysignal of frequency above 100 kilohertz. The device furthermorecomprises electronic means 8 able to detect modifications of theelectrical signal which are due to the presence of an electricallyconducting element, such as, for example, the finger of an operator, inproximity to the electrode array 4.

The electronic means 7 are, for example, linked to an electrode 4 by wayof an impedance 9 which can have a value of the order of 500 ohms to afew kilo-ohms. When the electrical signal is applied to an electrode 4,the behavior thereof can be compared with that of an impedance whosevalue is of the order of several hundreds of kilo-ohms at the frequencyof the specific electrical signal. On the other hand, when a conductingelement is arranged in the vicinity of the electrode 4, the latter thenbehaves as an impedance whose value decreases. This value may drop, forexample, down to 10 kilo-ohms, or even less. This value is dependent onthe position of the conducting element along the electrode 4. Here, oneexploits the fact that the electrodes 4 have a nonzero line impedancewhen a high-frequency electrical signal is applied to them. The closerthe conducting element is to an end 10 of the electrode 4, the endclosest to the impedance 9, the more the value of its impedance falls.Conversely, the closer the conducting element is to the other end 11,the so-called “outboard end”, the more the impedance of the electrodegrows. Specifically, the electrode 4 forms a resistive line whoseresistance increases with the distance separating the end 10 from thepoint of detection of the conducting element.

The measurement of variation of the impedance of the electrode 4therefore makes it possible to determine the position of the conductingelement along the electrode 4. This measurement may be made indirectlyby detecting, between the impedance 9 and the electrode 4, themodification of the specific electrical signal with the aid ofelectronic means 8. These means comprise, for example, an amplitudedemodulator 12 whose input 13 is connected between the impedance 9 andthe electrode 4. The output 14 of the amplitude demodulator 12 providesa central unit 15 with a signal representative of any modification ofthe specific electrical signal. The central unit 15 can compare thesignal from the amplitude demodulator 12 with a stored value table,which table gives the correspondence between the modification of theelectrical signal and the position of the conducting element along theelectrode 4.

The modification of the electrical signal as well as its detection havebeen described in relation to a single electrode 4, this making itpossible to determine the position of a conducting element along thiselectrode 4. Moreover, to completely determine the position of thesensitive element with respect to the touch surface 6, it is necessaryto know alongside which electrode 4 of the array the conducting elementis located.

The determination of the electrode 4 concerned may be effected by using,for each electrode 4, an impedance 9 and particular electronic means 8.This solution is unwieldy and, advantageously, the electrical signal isnot applied simultaneously but successively to the various electrodes ofthe array. This makes it possible to use an impedance 9 and means 8which are common to several electrodes 4 grouped together into a set ofelectrodes 4 in which the signal is applied successively. There may beone or more sets of electrodes 4 in one and the same array.

The redundancy of the detection may be improved. Specifically, matrixdisplays comprise at least two electrode arrays 4 and 5, as describedwith the aid of FIG. 1 a. It is advantageous to use these two arrays assensitive element of the touch surface. By using two electrode arrays 4and 5 which are, for example, orthogonal, it is moreover possible todetermine the dimensions of a conducting element placed in proximity tothe touch surface 6. Specifically, each electrode 4 or 5 influenced bythe conducting element makes it possible to define the distance betweenits end 10 and an extremity of the conducting element.

In a second variant, it is also possible to use the two electrode arrays4 and 5 in a simpler manner without seeking to determine the distanceseparating a conducting element from the end 10 of an electrode 4 or 5.The specific electrical signal is applied both to the electrodes 4 andto the electrodes 5. The central unit 15, in order to determine theposition of said region, defines this position as a function of at leastone electrode 4 and of at least one electrode 5 for which saidmodifications overstep a threshold.

In this case, one is content with determining whether or not aconducting element is present in the vicinity of an electrode 4 or 5. Byknowing at least one electrode 4 and at least one electrode 5, where theconducting element is detected, its position is determined in aCartesian reference frame whose measurement units are the electrodes 4for one direction and the electrodes 5 for the other direction. Thespecific electrical signals are then applied both to the rows and to thecolumns of electrodes 4 and 5, and the central unit 15 determines theposition of the conducting element as a function of at least oneelectrode 4 and one electrode 5 for which the modifications of specificelectrical signals overstep a threshold. The embodiment of the amplitudedemodulator is then simplified. It will simply have to deliver to thecentral unit 15 an item of information regarding the overstepping orotherwise of a threshold by the modified specific electrical signal.

In a third variant, described with the aid of FIG. 3, the display devicecomprises the electrode array 4, the electrode array 5, as well as means16 for driving the display. In this variant, the specific electricalsignal, generated by the means 7 (not represented in FIG. 3), is appliedsimultaneously to at least one row electrode 4 and to at least onecolumn electrode 5. Couplings between the row electrode 4 and the columnelectrode 5 are modified when the conducting element is in proximity tothe crossover between the row electrode 4 and the column electrode 5.The specific electrical signal is advantageously applied to a set formedby the two electrode arrays 4 and 5 diagonally.

More precisely, the electrodes 4 bear a serial number from 4-1 to 4-n.The same goes for the electrodes 5 which bear a number from 5-1 to 5-p.p and n represent integers. The electrical signal is appliedsuccessively to the electrodes 4 in the order from 4-1 to 4-n. At thesame time, the electrical signal is applied successively to theelectrodes 5 in the order from 5-1 to 5-p. The electrical signal isapplied simultaneously to at least one electrode 4 and to at least oneelectrode 5. Couplings between the electrode 4 and the electrode 5 aremodified when the conducting element is in proximity to the crossoverbetween the electrode 4 and the electrode 5. These couplings representan impedance formed between these two electrodes. At the start of asequence, the electrical signal is applied to the electrode 4-1 and tothe electrode 5-1. Thereafter, the electrical signal is applied to theelectrodes 4-2 and 5-2 and so on and so forth. When the numbers n and pare equal, this sequence continues until they are reached. When thesenumbers are different, for example when p is greater than n, theelectrical signal can be applied to an electrode 4-i and an electrode5-j and then at the following instant to the electrode 4-i again and tothe electrode 5(j+1). i represents an integer lying between 1 and n andj another integer lying between 1 and p. This double application of theelectrical signal to one of the electrodes 4 is repeated as often asnecessary such that, at the last instant of the sequence, the electricalsignal is applied to the electrodes 4-n and 4-p. If several doubleapplications are necessary, one chooses electrodes 4-i substantiallydistributed between 1 and n. It is thus possible to traverse a diagonalor possibly both diagonals of the display zone.

A measurement readout is thus obtained allowing map location, by virtueof the couplings existing between the electrodes 4 and the electrodes 5.More precisely, the map consists in storing the level of the electricalsignal, possibly modified by the presence of a conducting element, foreach pair of electrodes 4 and 5 for which the electrical signal isapplied simultaneously. The entire set of these levels forms a so-calledcurrent table. The current table is thereafter compared with severalprerecorded tables, each representing a detectable position of theconducting element in proximity to the display zone. When the currenttable comprises values substantially equal to those of a prerecordedtable, the position of the conducting element is deduced therefrom. Thismap can also be utilized, by exploiting the process described in Frenchpatent application FR 2 757 659 filed in the name of SEXTANT AVIONIQUEas if the proximity detection surface were continuous.

The electrical signal modification detected by the electronic means 8 isof low level and may be disturbed by numerous phenomena such as, forexample, electrical interference. To alleviate this problem, the displaydevice advantageously comprises electronic means able to aggregate themodifications of the electrical signal detected by the means 8. Theseelectronic means may be formed by the central unit 15. The aggregate iseffected over several neighboring electrodes. In practice, when theuser's finger is placed on the display, with a view to an action bymeans of the touch surface, it systematically covers several electrodes4, for example from 10 to 30 electrodes 4. There are therefore norepercussions in not taking account of a modification of the electricalsignal intervening on only one electrode 4, or even on a very restrictednumber of neighboring electrodes 4, for example 5 electrodes 4. Thecentral unit 15 can therefore interpret modifications of the electricalsignal, modifications which intervened on neighboring electrodes 4, as apresence of a conducting element, only when the modification concerns atleast a certain number of neighboring electrodes 4. The number ofelectrodes 4 is then determined by their spacing. In the same manner,modifications of the electrical signal which intervened on a largernumber of non-neighboring electrodes 4 will not be taken into accounteither.

It was seen previously, in the first variant, that the level of themodification due to the presence of a conducting element was dependenton the position of the conducting element along an electrode 4. It isconsequently possible to add an additional condition during theinterpretation of the modifications of the electrical signal whichintervened on several neighboring electrodes 4. The central unit 15 cantherefore interpret modifications which intervened on neighboringelectrodes 4 as a presence of a conducting element only when thesemodifications are of substantially equal level.

Advantageously, the specific electrical signal is applied successivelyto various electrodes 4 or 5. This makes it possible to avoid anycouplings between neighboring electrodes, more particularly betweenelectrodes of the same array. Specifically, the proximity of aconducting element modifies the impedance of an electrode in thevicinity of which it is located. This modification is generally veryweak and a coupling between two electrodes is liable to mask thismodification, hence the benefit of avoiding couplings betweenneighboring electrodes.

Furthermore, it has been noted, in the use of the first variant, thatthe level of modification, in this instance of attenuation, is not alinear function of the position of the conducting element along anelectrode 4. More precisely, for one and the same displacement of theconducting element along the electrode 4, the variation in the level ofthe electrical signal is larger in the vicinity of the end 10 of theelectrode 4, the end closest to the impedance 9 than in the vicinity ofthe end 11, the so-called free end of the electrode 4. Consequently, thesensitivity of the measurement of position of the conducting elementalong the electrode 4 is much better in the vicinity of the end 10.

To alleviate this defect, it is possible to exploit an interdigitatedstructure of the electrode array or arrays 4 used as sensitive element.With such a structure, the accuracy of the position of the conductingelement along several neighboring electrodes 4 will be obtained with theelectrode 4 for which the conducting element is closest to its end 10.

In the first variant, the use of the interdigitated structure also makesit possible to increase the redundancy of the measurements of theposition of the sensitive element along several neighboring electrodes4. The interdigitated structure furthermore makes it possible todiscriminate between two conducting elements placed simultaneously onthe touch surface 6 in proximity to several neighboring electrodes 4.Specifically, the electrodes 4 connected at their end 10 in the vicinityof an edge of the touch surface 6 make it possible to determine theposition of the conducting element closest to this end 10. On the otherhand, the electrodes 4 connected at their end 10 in the vicinity of theopposite edge of the touch surface will make it possible to determinethe position of the other conducting element.

Moreover, the set of influenced electrodes, when these arrays have aninterdigitated structure, makes it possible to define the contour of theconducting element. When an operator places both a hand and a finger onthe touch surface 6, the central unit 15 can use the informationdefining the contours of the hand and of the finger so as, for example,to take only the finger and not the hand into account.

It was seen previously that the conducting element may be the finger ofan operator. By way of variant, the conducting element can comprise aconducting stylus held by the operator. This stylus comprises an endthat the operator can place on the display. Advantageously, the surfacearea of this end is sufficient to cover up several neighboringelectrodes 4 or 5. The stylus affords electrical conduction between theend intended to be placed on the device and the body thereof held by theoperator. This makes it possible to modify the electrical signal appliedto the electrode or electrodes considered by capacitive effect. By wayof alternative, the stylus may be linked by a wire connection to theearth of the means 7 generating the electrical signal.

Advantageously, the specific electrical signal has a frequency above 100kilohertz. This makes it possible to use a capacitive effect to detectthe presence of the conducting element in proximity to the display zone.

Advantageously, the device comprises means 16 for driving the display.The means are known as a driver. The means 16 comprise a multiplexer 17intended to apply an excitation voltage 22 and the specific electricalsignal to an electrode 4 selected for the display. This makes itpossible to apply the specific electrical signal to the electrodeschosen for the proximity detection cyclically. More precisely, aspecific electrical signal is applied successively to the set ofelectrodes chosen in a predetermined order, then this application isrepeated in the same order, for as long as one seeks to detect theproximity of a conducting element.

An exemplary embodiment of the means 16 for driving the display isrepresented in FIG. 4. The means 16 comprise a multiplexer 17 whoseoutputs 18 are connected to the ends 10 of the electrodes 4. It is ofcourse understood that the means 16 may be used with the electrodes 5.The multiplexer comprises two inputs 19 and 20 to which voltage sourcesare connected. A voltage 22 that the multiplexer 17 sends to anelectrode 4 selected to carry out a display is available on the input19, by way of an impedance 21. A voltage 24 that the multiplexer 17sends to an electrode 4 not selected to carry out a display is availableon the input 20, by way of an impedance 23. The voltages 22 and 24 formthe electrical excitation of the layer 3. The input 19 is also connectedto the impedance 9 which belongs to the means 16. This input 19 is alsoconnected to the means 8 which are common to several means 16. The means8 are, consequently, exterior to the means 16. The impedances 9 and 21allow the superposition of the electrical signal sent by the means 7 andof the electrical excitation formed by the voltage sent to the selectedelectrode 4. The multiplexer 17 furthermore comprises an input 25controlling the multiplexer. To this input 25 is connected a link 26 onwhich flows a signal making it possible to select the electrode 4 whichreceives the voltage 22 and the electrical signal emanating from themeans 7 by way of the impedances 9 and 21.

A variant embodiment of the means for driving the display is representedin FIG. 5. This variant here bears the reference 30. As previously, themeans 30 comprise the multiplexer 17 and the impedances 9, 21 and 23.The multiplexer 17 receives the voltage 22 on its input 19 by way of theimpedance 21 and the voltage 24 on its input 20 by way of the impedance23. It also receives the link 26 on its input 25. Moreover, the means 30comprise the electronic means 7 generating the specific electricalsignal, the amplitude demodulator 12, advantageously synchronized withthe electronic means 7, an analog/digital converter 31 and an addressingmarker 32. The analog/digital converter 31 receives an item ofinformation representative of the modifications, which item ofinformation emanates from the amplitude demodulator 12 and provides adigital item of information to the central unit 15 which is exterior tothe means 20. The addressing marker 32 receives an information item fromthe multiplexer 17 making it possible to identify the electrode 4receiving the electrical signal. The addressing marker adapts thisinformation item so as to transmit it to the central unit 15. Thecentral unit 15 can then associate the modified electrical signalemanating from the analog/digital converter 31 and the electrode 4considered.

In FIGS. 4 and 5 described previously, the central unit 15 can be linkedto the multiplexer 17 by a link 33 allowing the central unit 15 tocontrol the multiplexer 17. The link 33 links each multiplexer 17 to thecentral unit 15. The link 33 supplements the link 26 which links the setof multiplexers 17 also to the central unit 15. Advantageously, themultiplexers 17 are linked in a chain by means of the link 26.

Advantageously, the specific electrical signal is superimposed on theexcitation. This makes it possible not to interrupt the excitationnecessary for the display to apply the specific electrical signal to theelectrode considered.

In certain display devices, for example bistable ones, the excitationnecessary for display is not applied regularly to the electrodes, butonly when the display is modified. The specific electrical signal canthen be applied to an electrode 4 or 5 when the excitation is notapplied to this electrode. Specifically, provision may be made for themeans 16 or 30 for driving the display to comprise a disabling switch 34making it possible either to apply the voltages 22 and 24 to the inputs19 and 20, or to link these inputs 19 and 20 to an earth 35. Thedisabling switch 34 is represented in FIG. 5. The input 19 neverthelessremains linked to the means 7. The disabling switch 34 is controlled bythe signal flowing on the link 26. When the inputs are linked to earth,the link 33 can still control the multiplexer 17 so as to apply thespecific electrical signal to the electrodes 4.

It will be readily seen by one of ordinary skill in the art thatembodiments according to the present invention fulfill many of theadvantages set forth above. After reading the foregoing specification,one of ordinary skill will be able to affect various changes,substitutions of equivalents and various other aspects of the inventionas broadly disclosed herein. It is therefore intended that theprotection granted hereon be limited only by the definition contained inthe appended claims and equivalents thereof.

1. An electronic display device comprising: means of detection ofproximity of a conducting element situated in proximity to a displayzone of the device; a set of row electrodes and of column electrodesscanning the display zone; means for generating an excitation of the rowelectrodes and of the column electrodes as a function of an image to bedisplayed on the display zone, comprising switches for applying theexcitation successively to each of the row electrode and to each of thecolumn electrodes; means for applying a specific electrical signaldistinct from the excitation successively to each of the row electrodeand to each of the column electrodes through the switches, means forcontinuously detecting modifications of the specific electrical signalwhich are induced by the presence of a conducting element in proximityto a region of the display zone, and means for determining the positionof said region as a function of said detected modifications.
 2. Thedevice as claimed in claim 1, wherein the row electrodes and the columnelectrodes respectively form two distinct arrays, in that at least onearray of electrodes is chosen for the proximity detection, and in thatthe means for determining the position of said region define thisposition as a function of the level of said modifications intervening onthe chosen array.
 3. The device as claimed in claim 1, wherein thespecific electrical signal is applied both to the rows and to thecolumns, and in that the means for determining the position of saidregion define this position as a function of at least one row and of atleast one column for which said modifications overstep a threshold. 4.The device as claimed in claim 1, wherein the electrical signal isapplied simultaneously to at least one row electrode and to at least onecolumn electrode and in that couplings between the row electrode and thecolumn electrode are modified when the conducting element is inproximity to the crossover between the row electrode and the columnelectrode.
 5. The device as claimed in claim 4, wherein the specificelectrical signal is applied to said set diagonally.
 6. The device asclaimed in claim 5, wherein the electrical signal is applied to said setalong two diagonals of the display zone.
 7. The device as claimed inclaim 1, wherein the means for determining the position of said regiontake no account of the modifications unless they intervene on severalneighboring electrodes.
 8. The device as claimed in claim 1, wherein thespecific electrical signal is applied successively to variouselectrodes.
 9. The device as claimed in claim 1, wherein the electrodesare interdigitated.
 10. The device as claimed in claim 1, wherein theconducting element comprises a stylus.
 11. The device as claimed inclaim 1, wherein the specific electrical signal has a frequency above100 kilohertz.
 12. The device as claimed in claim 1, wherein itcomprises means for driving the display, and in that these meanscomprise a multiplexer intended to apply an excitation voltage and thespecific electrical signal to an electrode selected for the display. 13.The device as claimed in claim 12, wherein the means for driving thedisplay furthermore comprise means generating the specific electricalsignal, an amplitude demodulator and an analog/digital converter, theamplitude demodulator receiving the specific electrical signal andproviding the analog/digital converter with a signal representative ofsaid modifications.
 14. The device as claimed in claim 1, wherein thespecific electrical signal is superimposed on the excitation.
 15. Thedevice as claimed in claim 1, wherein the specific electrical signal isapplied to an electrode when the row and column electrodes are notselected for region detection.
 16. The device as claimed in claim 1,wherein the first electrode array is formed from the row electrodes andis situated between a plate and a layer and a second electrode arrayformed from the column electrodes is situated between another plate andthe layer and wherein electrical excitation of the layer is achieved byapplying a potential difference between an electrode of each array. 17.The device as claimed in claim 1, wherein drivers are used for drivingthe display to apply the excitation voltage and the specificationelectrical signal to an electrode selected for the display.
 18. Thedevice as claimed in claim 1, wherein the device comprises means fordriving the display such that drivers are used to apply the excitationvoltage and the specific electrical signal to an electrode selected forthe display.